The technical field of the present invention relates to cooling of avionics and/or power electronics, i.e. electronics designed for use in aerospace vehicles, such as aircraft electronics. The avionics must be cooled constantly or they will overheat. Fuel or air cooling cycles are typically used for cooling of avionics. In rare cases vapour cooling circuits are used.
Air cooling circuits utilise compressed air from the aircraft engine, which is converted to be suitable for avionics cooling (temperature, pressure and humidity), and for keeping the cabin environment comfortable and pressurised. Air cooling of avionics is very energy consuming. The coefficient of performance is about 0.10-0.25, i.e. in order to withdraw a heat load of 10 kW in the avionics 40-100 kW needs to be taken from the engine.
Fuel cooling circuits utilise the aircraft fuel for direct cooling of the avionics or by means of a separate cooling circuit, in which heat is transferred from the avionics to the fuel in a heat exchanger. Fuel cooling systems are usually very energy effective. A power of 1-2 kW may be sufficient to operate a system which is to withdraw a heat load of 10 kW. However only a limited amount of heat can be transferred to the fuel, without reaching the upper limit of the fuel temperature, or that the fuel temperature raises such that it becomes unsuitable for avionics cooling.
Studies have shown that vapour cooling cycles are the most energy effective systems for cooling of avionics. The coefficient of performance is generally 1-3 (i.e. 3-10 kW needs to be taken from the engine in order to withdraw a heat load of 10 kW in the avionics).
Cooling cycles of the above types can also be combined with each other in various configurations. An example of such a combined cooling system is the system for environmental control in an aircraft shown in U.S. Pat. No. 6,948,331, which includes a number of cooling cycles connected to each other. One of the cycles is an avionics cooling loop, by means of which heat withdrawn from the avionics is transferred to an air flow of an environmental air cooling cycle. A vapour cooling cycle and an air/fuel heat exchanger are used to transfer heat from the air flow to a fuel flow, which is subsequently conducted to the engine. This system is adapted to the different conditions that occur when the engine is running or not. However, it does not take account to conditions that may arise due to variations in the heat load of the avionics. The system is also quite complicated.